1. Field of the Invention
The embodiments of the invention disclosed herein relate generally to the field of diagnostic and therapeutic medical procedures involving the intravenous infusion of fluids such as contrast-enhanced radiographic imaging as an example and, more particularly, to a system capable of controlled proportional mixing and delivery of fluid mixtures to a patient. In one specific application, contrast media may be proportionally mixed with another fluid such as saline for continuous delivery to a patient undergoing a medical radiographic imaging procedure.
2. Description of Related Art
In many medical diagnostic and therapeutic procedures, a medical practitioner such as a physician injects a patient with a fluid. In recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of fluids, such as contrast media (often referred to simply as “contrast”), have been developed for use in procedures such as angiography, computed tomography (“CT”), ultrasound, and NMR/MRI. In general, these powered injectors are designed to deliver a preset amount of contrast at a preset flow rate.
Angiography is an example of a radiographic imaging procedure wherein a powered injector may be used. Angiography is used in the detection and treatment of abnormalities or restrictions in blood vessels. In an angiographic procedure, a radiographic image of a vascular structure is obtained through the use of a radiographic contrast medium which is injected through a catheter. The vascular structures in fluid connection with the vein or artery in which the contrast is injected are filled with contrast. X-rays passing through the region of interest are absorbed by the contrast, causing a radiographic outline or image of blood vessels containing the contrast. The resulting images can be displayed on, for example, a video monitor and recorded.
In a typical contrast-enhanced radiographic imaging procedure such as angiography, the medical practitioner places a cardiac catheter into a vein or artery. The catheter is connected to either a manual or to an automatic contrast injection mechanism. A typical manual contrast injection mechanism includes a syringe in fluid connection with a catheter connection. The fluid path also includes, for example, a source of contrast, a source of flushing fluid, typically saline, and a pressure transducer to measure patient blood pressure. In a typical system, the source of contrast is connected to the fluid path via a valve, for example, a three-way stopcock. The source of saline and the pressure transducer may also be connected to the fluid path via additional valves, again such as stopcocks. The operator of the manual system controls the syringe and each of the valves to draw saline or contrast into the syringe and to inject the contrast or saline into the patient through the catheter connection.
Automatic contrast injection mechanisms typically include a syringe connected to a powered injector having, for example, a powered linear actuator. Typically, an operator enters settings into an electronic control system of the powered injector for a fixed volume of contrast and a fixed rate of injection. In many systems, there is no interactive control between the operator and the powered injector except to start or stop the injection. A change in flow rate in such systems occurs by stopping the machine and resetting the injection parameters. Automation of contrast-enhanced imaging procedures using powered injectors is discussed, for example, in U.S. Pat. Nos. 5,460,609; 5,573,515; and 5,800,397.
It is often desirable to deliver a mixture of contrast and a diluent such as saline to the patient undergoing the radiographic imaging procedure. Depending on a patient's particular physical characteristics, age, and the tissue to be imaged, the desirable concentration of contrast media varies. Medical practitioners can purchase pre-mixed solutions of contrast media in various discrete concentrations and this is a common practice in the medical field. Presently, contrast media is provided in sterilized glass bottles ranging in size from 20 ml to 200 ml. Plastic packages are also available. Presently used contrast media containers are single use which means that once a container is opened its contents must all be used for one patient and any residual unused contrast and the bottle must be discarded. As a result, a medical facility must purchase and stock many concentrations in multiple container sizes to provide the right amount of the right contrast concentration for a specific procedure while minimizing wastage of contrast remaining in any opened containers. This multitude of sizes and concentrations increases costs throughout the contrast supply chain. Contrast manufacturers are required to make many batches with various concentrations and package each in differently sized containers. The manufactures must have inventories of each concentration/container size on hand to quickly meet their customers' requests. Each concentration level and container size also entails an added regulatory burden.
In the end-use medical facility environment, there are additional costs due to the efforts required to purchase and stock various concentration/container sizes. Bulk storage space is required for stocking and cabinets are required in each procedure room. Moreover, labor and time are required to make sure the correct numbers of each container are kept in each procedure room. Finally, the present system results in waste and/or less than optimal studies if this complicated logistics chain fails at any point.
Presently, most medical facilities utilize a standard protocol for a given set of indications. For instance, for a CT scan of the liver, the protocol may call for 130 ml of contrast injected at 3 ml/s. This protocol is used for a wide variety of patient weights and physical conditions. One goal of this standardization is to minimize errors. Another goal is to decrease the likelihood of having to repeat the procedure, with the accompanying additional radiation and contrast dose to the patient. However, there are costs associated with this method. Many patients may get more contrast than they need for an image to be diagnostic. Overdosing wastes contrast but there is no way with the present contrast supply and delivery system to remedy this without stocking many more sizes of containers and being more judicious in the filling of injection syringes. Other patients may have studies that are less than optimal as they do not receive enough contrast and there is a much greater chance of having to repeat the procedure.
In angiography, there are no set protocols to the same extent as in CT because patient size determines vessel size which in turn determines the volume and flow rate required. This means that a fixed amount of contrast cannot be prepared ahead of time with any confidence that more will not be needed during the procedure or that a significant amount will not remain and be wasted at the end of the procedure. To avoid delays during an angiography procedure, the medical practitioner typically loads more contrast than the average amount to be used with the realization that some contrast is likely to be wasted.
A further result of the foregoing system is the accumulation of a significant amount of hazardous medical waste at the conclusion of the procedure. To save contrast, several small glass bottles may be opened per patient, one or more plastic syringes may be used, and various tubing arrangements may be used. Each of these items has an associated cost to purchase the item and an associated cost to properly dispose of the item.
Solutions have been proposed to overcome the foregoing problems associated with the use of a multiplicity of concentrations and container sizes and, further, to allow for more individualized contrast mixtures to be produced to meet individual patient requirements. For example, U.S. Pat. Nos. 5,592,940 and 5,450,847 to Kampfe et al. disclose a mixing system that allows for mixing contrast medium and saline “on site” at a medical facility. More particularly, the Kampfe et al. patents disclose an exemplary mixing system that involves withdrawing or removing predetermined amounts of contrast medium and a diluent (e.g., saline) from respective vessels and mixing these fluids in a mixing chamber and then delivering the mixed fluid to a suitable receiving container, such as a vial, bag, or syringe which is used to deliver the mixed fluid to a patient. Other contrast-diluent mixing systems are known from U.S. Pat. Nos. 6,901,283 to Evans, III et al. and 5,840,026 to Uber, III. et al., the disclosures of which are incorporated herein by reference. U.S. Pat. No. 7,060,049 to Trombley, III et al. discloses a system for injecting a multi-component enhancement medium into a patient that incorporates an agitating mechanism to maintain the medium in a mixed state for injection and this patent is also incorporated herein by reference. Within the representative “mixing” systems disclosed in the foregoing patents, simple mechanical mixing devices are used to mix the respective fluids. For example, in the systems disclosed by Evans, III et al. and Uber, III et al., the fluids to be mixed are joined together as they flow through a static mixer that contains helical vanes. In the Kampfe et al. patents, a bulk mechanical mixer is used to mix two sequential flows. In each of these cases, fluid mixture proportions are determined by controlled metering valves or other devices (e.g., peristaltic pumps) in the flow path.
Other devices are known for use in fluid delivery systems having medical applications to mix and dispense a mixed fluid, for example, in preset and “fixed” concentration ratios. For example, a selector valve such as that disclosed in U.S. Pat. No. 3,957,082 to Fuson et al. is known to allow an operator to “dial-in” a selected fluid choice or mixture of fluids in a preset or predefined ratio. The Fuson et al. patent allows for the choice of a first fluid such as a drug, a second fluid such as saline, or preset “fixed” mixture ratio of the two fluids (e.g., a 50%-50% mixture) for delivery to a patient. U.S. Pat. No. 6,918,893 to Houde et al. discloses a selector valve having specific application in the delivery of contrast and saline in contrast-enhanced radiographic imaging procedures but this selector valve does not have the ability to dial in a desired mixture ratio of two fluids. The disclosure of U.S. Pat. No. 3,957,082 is incorporated herein for the selector valve teaching of this disclosure.
Double or dual pinch valves are also known for use in fluid handling systems to accomplish one or more of: alternating the flow of two fluids, blocking flow of the two fluids, or permitting simultaneous flow of the two fluids in a fluid path as disclosed in U.S. Pat. Nos. 2,985,192 (Taylor et al.); 3,411,534 (Rose); 3,918,490 (Goda); 4,071,039 (Goof); 4,259,985 (Bergmann); and 4,484,599 (Hanover et al.). U.S. Pat. No. 6,871,660 to Hampsch discloses a solenoid operated double or dual pinch valve to provide alternating flow capability in a devices used in medical and pharmaceutical laboratory research. The various double or dual pinch valves disclosed in the foregoing patents, as indicated, have the ability to control the flow of the respective fluids through two channels by pinching none, one, or both of the channels through the pinch valve. Accordingly, these pinch valves allow for one channel to be completely open and the other to be completely closed so as to allow only one fluid to pass through the pinch valve, allow for both channels to completely open, or completely block both channels. As a result, these pinch valves provide no ability to mix or control the proportional mixing of two or more fluids in any desired proportion as provided in the embodiments disclosed herein in this disclosure. Such ability to mix or, more clearly, control the proportional mixing of two fluids has been attempted by varying the respective speeds at which two respective pump devices deliver fluids to a mixing fluid path, such as disclosed in U.S. Pat. No. 3,935,971 to Papoff et al., but such a system is in practice difficult to control as it involves regulating precisely motor speed of the motors driving the respective pump devices. As a result, such controlled, dual pump systems do not present a very accurate proportioned mixture to the output or delivery conduit. The foregoing shortcomings are overcome by the various embodiments described herein.